The 35-year-old, with Mourinho’s men pushing for a winner in the second half against Blackburn Rovers, was thrown on with 28 minutes and duly came up with a winner.
The Spain international also had his say on the importance of the FA Cup, as United look to beat Chelsea in order to reach the semi-final.
And Herrera, speaking to ManUtd.com, noted that the Portuguese knows exactly when to introduce Zlatan at Old Trafford.
“We know how important he is for us,” Herrera said. “I think our manager knows exactly when he is important and when he can be decisive for us. And he did it, he scored a fantastic goal from a fantastic pass from Paul.”
Cup ties away at Championship sides can be a pretty galling experience. Normally, Premier League sides will find their flow and stroll to a comfortable win, but every now and again the whole encounter can be a truly scrappy, bitter affair.
And Mourinho, for all the criticism he receives, is no novice to English football. He could tell from the sidelines at Ewood Park that the tempo needed to change, and so on came Zlatan, accompanied by Paul Pogba, to decide the encounter once and for all.